Jessica is 9 years older than Omar. Five years ago, Jessica was 4 times as old as Omar. How old is Omar now?
Explanation: We can use the given information to write down two equations that describe the ages of Jessica and Omar. Let Jessica's current age be $j$ and Omar's current age be $o$ The information in the first sentence can be expressed in the following equation: $j = o + 9$ Five years ago, Jessica was $j - 5$ years old, and Omar was $o - 5$ years old. The information in the second sentence can be expressed in the following equation: $j - 5 = 4(o - 5)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $o$ , it might be easiest to use our first equation for $j$ and substitute it into our second equation. Our first equation is: $j = o + 9$ . Substituting this into our second equation, we get the equation: $(o + 9)$ $-$ $5 = 4(o - 5)$ which combines the information about $o$ from both of our original equations. Simplifying both sides of this equation, we get: $o + 4 = 4 o - 20$ Solving for $o$ , we get: $3 o = 24$ $o = 8$.